Apparatus for making filament reinforced plastic screen

ABSTRACT

Filament reinforced cylindrical plastic screens having open slots defined by their surface wires which are of substantially different widths can be produced on a single helically finned mandrel. The slot widths are varied in accordance with the amount of wire-forming material placed in the generally V-shaped grooves defined by the mandrel fins. The grooves have a double relief angle so that the lower support portions of the surface wires will be formed so as to have a slightly tapered, radially elongated cross-section and the upper portions of the wires will have their sides at a substantially greater relief angle. This relationship permits a relatively small change in the total height of the wires to have a substantial effect on the width of the top portion of the wires, and thus, on the width of the slot openings which can be formed between adjacent wires.

This is a division of application Ser. No. 334,105, filed Dec. 24, 1981now U.S. Pat. No. 4,381,820.

BACKGROUND OF THE INVENTION

The invention relates to filament wound, reinforced plastic screens ofthe general type disclosed in Shobert U.S. Pat. No. 3,658,128 and in myco-pending Wagner et al. application Ser. No. 244,382, filed Mar. 16,1981 now U.S. Pat. No. 4,378,294. The latter application is assigned tothe same assignee as the present application and its disclosure ishereby incorporated by reference into the present application. Moreparticularly, the invention relates to the production of filament woundscreens on a finned mandrel with the screens being produced so as tohave different slot widths to accommodate different expected useconditions. For example, one situation might require a slot width of0.050", while another might require a slot width of 0.100" or even0.150". In the aforementioned Shobert U.S. Pat. No. 3,658,128, it isapparent that any width of slot requires a turning down of the finishedscreen cylinder. Such a machining operation would naturally cut manyfibers and destroy the protective resin coating over them, thus makingthe cut ends porous to water or other liquids which, in the absence ofan additional protective coating, could wick along the fibers anddeteriorate them. The large side surface relief angles on thetriangularly shaped Shobert wires permit a relatively large change inslot width. However, the triangular wire shape shown would result in alarge loss of wire material as the screen is turned down in diameter inproducing a wide slot. The screen would also exhibit a substantial lossin collapse strength when formed with wide slots since the collapseresistance of the screen varies with the 3rd power of the effectivethickness of the wire in the radial direction. The much smaller sidesurface relief angles disclosed in the aforementioned co-pendingapplication permit the surface screen wires to be wound at a much closerpitch, thus permitting larger percentages of screen "open area" than theShobert wires since the wires are much narrower and more closely pitchedthan Shobert's. However, the small relief angle greatly limits the rangeof slot widths that can be produced on a given mandrel. This is so sincethe slot width is changed by winding larger or smaller amounts offilaments in the space defined by the helical grooves of the mandrel,thereby changing the radial height of the wire. The narrow relief anglerequires a relatively large change in the radial height of the wire toachieve a relatively small change in slot width. Thus, for a givenmandrel to be able to produce screens having a predetermined minimumcollapse resistance in a given range of slot widths, the narrowest slotscreens would have a much larger radial dimension than the widest slotscreens and a much greater collapse strength than necessary.

SUMMARY OF THE INVENTION

It is among the objects of the present invention to provide a filamentwound screen of a given nominal diameter which can be produced in a widerange of slot width dimensions on a single mandrel. It is a furtherobject to provide such a screen which will require a relatively smallchange in diameter to produce a substantial change in slot width. It isa still further object to provide such a screen and an apparatus andmethod of making it so that relatively large amounts of slot open areaand a high collapse strength can be achieved with minimal amounts ofmaterial being used.

These and other objects are achieved by the apparatus of the presentinvention in which the side wall surfaces of the tapered fins orprojections on the mandrel which form the helical screen surface wiresare provided at their radially innermost portions with a small reliefangle and at their radially outermost portions with a much larger reliefangle. These different relief angles cause the inner portion of thescreen wire, which comprises the major portion of the total screen wallthickness, to be relatively narrow in cross-section and to have a smallrelief angle, such as about 3°, for example. The inner portion providesthe basic collapse resistance of the screen. The outer portion of thescreen wire has a much larger relief angle, such as about 15°, forexample. The large relief angle provides a minimal wall thickness changefor a given slot dimension change.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing a mandrel of a type suitable for makingthe screen of the present invention;

FIG. 2 is a side view, partially sectioned, of a screen incorporatingthe present invention;

FIGS. 3a and 3b are enlargements of several of the mandrel projectionsor fins on the mandrel of FIG. 1 showing their relationship to filamentswound thereon to form screen wires having wide and narrow screen slots,respectively;

FIGS. 4a and 4b are similar to FIGS. 3a and 3b except they show screenwires having wide and narrow screen slots which have been formed on amandrel of the type disclosed in the aforementioned co-pendingapplication;

FIGS. 5a and 5b are similar to FIGS. 3a and 3b except they show screenwires having wide and narrow screen slots which have been formed on amandrel of the type disclosed in the prior art Shobert U.S. Pat. No.3,658,128.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a mandrel suitable for use in making the filamentwound screen of the present invention is indicated generally at 10. Themandrel 10 is of the type shown in the aforementioned co-pendingapplication in that it has a removable smooth surfaced end portion 12, aremovable threaded end portion 14 and a plurality of finned segments 16containing fin portions 18. The mandrel elements are all mounted on acylindrical base member (not shown) which is adapted to be removed whenthe fin segments 16 are collapsed inwardly after a screen is formedthereon. The fin portions 18 on each segment 16 are uniformly spacedfrom each other and the fin portions on all of the segments, whenassembled, lie on the locus of a helix. The spaces 20 between axiallyadjacent fin portions 18 define the shape of the resin coated filaments(not shown) which are wound therein to form the wire wrap portions of ascreen. As explained in the aforementioned application, a single bundleof resin coated filaments can be wound longitudinally between thetoothed end projections 24 and the pin projections 26 andcircumferentially to produce a screen member 30 which is of the formshown in FIG. 2 except that the male threads 32' on the male end portion32 are formed by a turning tool. The female end portion 34 of the screen30 has an internal thread 34' which is integrally formed on the threadedend portion 14 of the mandrel. The intermediate slotted portion 36 ofthe screen comprises helically wound screen wire portions 38 whichdefine slot openings 40. The wires 38 are supported in spaced relationto each other by support rod portions 42.

FIGS. 3a and 3b are enlarged cross-sections showing several of the fins18 of FIG. 1. It can be seen that the fins 18 have their base wallportions 18a positioned at a small relief angle α and their tip wallportions 18b positioned at a much larger relief angle β. As seen in FIG.3a, the provision for double relief angles permits screen wires 38 to beformed with a wide screen slot space ω₃₈ such as 0.150" and a relativelytall cross-section at a relatively close pitch P₁₈ of 0.400", forexample, since the relief angle β is preferably quite small, such as 3°.Since the relief angle β is much larger, such as 15°, it can be seen inFIG. 3b that when the screen wires 38' are made deeper so as to producea relatively narrow screen slot space ω'₃₈, such as 0.050", the amountof additional depth required is much less than if wall surface 18b wasat the same small angle as surface 18a. Referring to FIGS. 4a and 4bwherein the fins 118 have a constant angle γ of about 15°, it can beseen that it is possible for screen wires 138 to be formed with 0.150"slots, ω₁₃₈ or for wires 138' to be formed with 0.050" slots, ω'₁₃₈.However, the pitch P₁₁₈ between fins 118 must be increased from 0.400"to 0.500" to accommodate such a range of slot widths. The prior artdesign shown in FIGS. 5a and 5b requires that the pitch P₂₁₈ betweenfins 218 be increased even further, to 0.850", in order to accommodate arange of slot widths ω₂₃₈, ω'₂₃₈ from 0.050"-0.150".

If one assumes that the various mandrel fins shown in FIGS. 3a, 3b, 4a,5a and 5b are sized and pitched so as to produce a screen having a 16.0"outside diameter when the screen slots are 0.150" and so as to permitscreen slot openings in a range from 0.050-0.150" and a minimum criticalcollapse pressure of the resulting screen of 75 psi, it can be readilycalculated that the improved dual-relief angle design of FIG. 3b hassignificant advantages. For example, the wires 38, 38' have respectivecross-sectional areas of 0.0923" and 0.1484", as compared to 0.108" and0.183" for 138, 138' or 0.212" and 0.277" for 238, 238'. The smallercross-section of the FIGS. 3a, 3b embodiments requires fewer windingpasses and less material to produce. The FIGS. 3a, 3b embodiments alsohave a substantially greater open area of the screen slots ω₃₈, ω'₃₈ perunit of length of screen. Thus, for a given length of screen, much lesspumping energy would be required to pass a given volume of liquidthrough the screen. Alternatively, the same amount of total open slotarea could be achieved with less footage of screen. More specifically,for the examples shown in FIGS. 3a, 3b, 4a, 4b, 5a and 5b, respectively,the open area, in percent of total length, can be calculated to be28.5%, 9.6%, 22.8%, 7.7%, 13.4% and 4.5%. The critical collapse pressureof the aforementioned 6 screen examples can be calculated, respectively,to be 95 psi, 272 psi, 77 psi, 220 psi, 100 psi and 164 psi. Althoughthe FIG. 5a embodiment is slightly better in this regard, the FIGS. 3aand 3b embodiments substantially exceed the FIGS. 4a, 4b and 5bembodiments in collapse strength. The calculations were made using theaforesaid dimensions and angles and assuming a maximum wire width andwire height for the respective six embodiments 3a-5b of 0.250", 0.500";0.350", 0.687"; 0.350", 0.500"; 0.450", 0.687"; 0.700" , 0.606"; and0.800", 0.693".

One additional advantage of the invention shown in FIGS. 3a, 3b comparedto the FIGS. 5a, 5b embodiments is the fact that there is a relativelylarge difference between the heights of wire 38 and wire 38' as comparedto the difference between 238 and 238'. Thus, a small variation in theamount of material wound between fins 18 in attempting to achieve agiven small slot width ω'₃₈ will have much less effect on achieving thedesired slot width than would be true in the case of FIG. 5b where verysmall changes in the height of wire 238' can produce quite large changesin the slot width ω'₂₃₈.

It is preferred that the angle α at which the major portion 18a of thelength of the side of fin 18 is formed be no greater than about 5° andpreferably no greater than about 3°. Some angle is necessary tofacilitate withdrawal of the mandrel segments radially inwardly of thescreen after the screen is wound and cured. However, too large an angleα is wasteful of material since the ability of the screen wires 38, 38'to resist collapse depends to a much greater extent on the height of thewire than on its width. It is also preferred that the angle β at whichthe minor portion 18b of the length of the side of fin 18 is formed beat least 10° and preferably about 15°. Since the side wall portions ofthe wear surface portion of the wires 38, 38' is formed by the wallportions 18b, it can be seen that having a smaller angle β would make itnecessary to make the wire 38' much taller in order to enable a singlemandrel to make the variation in slot sizes ω₃₈, ω'₃₈, shown in FIGS.3a, 3b. The extra height would add unneeded collapse strength for smallslot opening screens at the expense of requiring much additionalmaterial. However, angle β should not be too large either since it wouldthen be difficult to obtain a desired uniform slot width ω'₃₈ since itis not possible to exactly fill every groove between adjacent fins 18with the identical volume and density of resin coated filamentarywrapping material.

I claim as my invention:
 1. In a screen winding apparatus of thecollapsible, plural segment, helically finned mandrel type used forforming a strand of resin-coated reinforcing filaments into a helicallywound screen surface defining wire, the improvement comprising providingfins on the mandrel segments which are formed so that the major portionof the radial length of their sides, when viewed in an axial plane ofthe mandrel, starting at their base, is tapered in an outwardlyconverging direction at a relatively small angle and the remaining minorportion of their radial length is tapered at a relatively larger angle,said minor portion being adapted to be engaged along lesser or greaterportions of its radial extent by lesser or greater thicknesses of resincoated reinforcing filaments, depending upon the width of screen slotdesired between adjacent helically wound screen wires formed betweenadjacent fins on the mandrel, whereby said major portion of the finradial length will produce a relatively narrow width, slightly taperedsupport base portion on said screen wires while said minor portion ofthe fin radial length will produce a substantially wider wear surface.2. The screen winding apparatus of claim 1 wherein the angle of taper ofsaid major portion of the radial length of said fins is no greater thanabout 5°.
 3. The screen winding apparatus of claim 1 wherein the angleof taper of said major portion of the radial length of said fins is nogreater than about 3°.
 4. The screen winding apparatus of claim 3wherein the angle of taper of said major portion of the radial length ofsaid fins is at least 10°.
 5. The screen winding apparatus of claim 3wherein the angle of taper of said major portion of the radial length ofsaid fins is about 15°.